Don't freak out if trying to close a socket that was already closed.

lib/roles/provider.js

@@ -365,8 +365,11 @@ module.exports = function(options) {
   lifecycle.observe(function() {
     clearTimeout(totalsTimer)
 
-    push.close()
-    sub.close()
+    try {
+      push.close()
+      sub.close()
+    }
+    catch (err) {}
 
     return Promise.all(Object.keys(workers).map(function(serial) {
       return workers[serial].cancel()